Tory MP Anne-Marie Trevelyan said: “I believe that individuals who have subscribed to Open Britain should be acutely aware of any correspondence they receive during the General Election period, and report anything they believe is wrong to the [Information Commissioner’s Office].”

A spokeswoman for the information watchdog told City A.M. today that it had not received any complaints over the campaign.

“Political organisations need to be transparent with people’s data but it’s also important that people are aware of what they are signing up to before handing over their personal information. Asking more questions at the sign-up stage means people may be able to identify when their information has been misused,” they added.

“Our message to the public is that if people have concerns about the way their information has been used, they can raise them with the ICO.”

An Open Britain spokesman said: “As an organisation with over half a million supporters, we take our data protection responsibilities very seriously.

“We always abide by all the rules governing our use of data and will, of course, continue to do so during the General Election.”

Former education secretary Nicky Morgan, former business minister Anna Soubry and former attorney general Dominic Grieve all cut ties with the campaign.

In a statement, the trio said: “As long standing Conservative Party members and MPs it is untenable for us to play any further role in an organisation, such as Open Britain, which is advocating campaigning against Conservative MPs or candidates.”